Started furnace checked temp rise insured proper operation of the humidifier customer had already replaced pad left spare on site tested and inspected all electrical components and controls and cleaned flame sensor and condensate trap performed combustion analysis and found co was to high due to a small crack at the heat exchanger checked for co in air stream and found none informed customer that heat exchanger was failing and due to the cost of repairs and the age of the furnace highly recommended that customer replace the system customer had a quote made up from Mike on 8-03-17 Greg is looking into it and will contact customer with further details.